Cold Cranking Amps for engine start battery
Can anybody tell me how you can calculate the CCA for an engine?

John B
Swan 411 010

Dear John
You have the M65 engine, and the manual does not give CCA but says: "A suitable battery for the M65, if specified by BS3911, will supply a minimum current of 340 A (for 60 seconds, with the voltage not falling below 8.4 V, at minus 18 C)"
Suggest you present this to the battery supplier.
Kind regards
Lars

Lars, I asked the question because as you state the manual does not specify the CCA.

John B

John,
I would simply suggest you to install a battery of a capacity bigger than the previous one. Simply because you are facing this problem, it might be wiser to consider this option.
You may read something regarding this topic here:
http://www.ybw.com/forums/showthread.php?150591-How-do-I-calculate-the-CCA-for-my-engine
Regards,
Matteo45 (Grampus 47/016)

John,
Unfortunately there is no way of theoretically computing what you ask because the involved physiochemical phenomena are strongly non linear and only direct measurements will give meaningful data. Moreover the battery manufacturers are very jealous of their data.
Notwithstanding, I want to pinpoint that the technical definition of CCA is a very close relative of what your manual states.
As a rule of thumb I suggest to assume that the required cranking amperage should not exceed 3CA, i.e. three times the number that defines the capacity of the battery in Ah. In your case this means that the battery capacity should be at least 115 Ah. In order to be on the safe side and, in particular, to take into account that the nominal capacity decreases with battery age, you may want to increase this number by a certain percentage.
Good luck!
Daniel, 411/004

Daniel, Lars, I am also now advised that when using Gel and AGM batteries for the engine start function that there C.C.Amps performance is greatly improved by a factor of 50% so that you can reduce the amps of the battery.

Any thoughts on this?

John B
Swan 411 010

John,
as in the other post: what they told you seems a bit exaggerated regarding AGM batteries, and, for what I recall, is totally false for GEL batteries.
Please double check the actual specifications of the manufacturers; although, as I wrote, they are "jealous" of their data, they cannot lie about the CCA written on the labels of their batteries!
Daniel, 411/004